1. Field
The following description relates to a semiconductor device. The following description also relates to a super junction semiconductor device, including one cell as a whole by connecting with each other a pillar region of an active region and a pillar region formed in a termination region that surrounds the active region without floating.
2. Description of Related Art
In alternatives, a high voltage device and a high power device are used in a power IC device for electric power conversion and in an electric control system. For example, a planar gate type MOSFET is used frequently as an IC device.
A cross sectional diagram of a unit cell of a general planar gate type metal-oxide-semiconductor field-effect transistor (MOSFET) is shown as FIG. 1. A MOSFET is a type of transistor used for amplifying or switching electronic signals. In FIG. 1, a breakdown voltage of a device is determined by a depletion layer formed between a P+ and an N-Epi region by a voltage applied on a drain when a gate voltage and a source voltage are identical.
However, the planar gate type MOSFET is to be designed to sustain over certain thicknesses and concentrations for the N-Epi region, such as to sustain an electric field distribution namely, a breakdown voltage. However, it is difficult to have a component below a certain resistance because of the relationships with the electric field distribution. Especially in the case of a 500 V level MOSFET, such a device has a problem of on-resistance growing larger as a breakdown voltage increases because almost 90% of an on-resistance component is epi resistance. Although measures to improve design or optimize epi resistance are sought after in order to reduce on-resistance, such measures did not produce much improvement.
Thus, a semiconductor device having a super junction structure is proposed. A super junction semiconductor device is similar to a general MOSFET gate and a P-type WELL structure. However, a super junction semiconductor device has a structure of a P-type pillar region formed in an N-type epi layer of a lower P-type body region, and a remaining N-type epi layer becomes an N-type pillar region in order to have a super junction feature. Thus, when a voltage is applied on a drain side, unlike a general MOSFET, which only extends vertically, a depletion layer of the super junction semiconductor device extends both vertically and horizontally. At this time, when both regions become identical, both the N region and the P region become completely depleted, and hence are able to receive a high breakdown voltage. Also, in this example, a horizontal electric field is theoretically generated constantly since electric charge does not exist vertically.
However, when a pillar in floating state on termination region exists in a super junction semiconductor device, the level of charge compensation becomes different in comparison to the adjacent pillar.
Referring the example of FIG. 2, some pillars 12 among the pillars 12, 14 are formed on an N-type epi layer 2 of an N-type substrate 1, such that the pillars 12 are connected to a source contact region 10 and the rest of the pillars 14 are connected to a field oxide layer 20. The pillars 14 connected to the field oxide layer 20 are the pillars in a floating state. In other words, FIG. 2 shows the case of groups of pillars existing alone that are not connected with each other.
When a pillar 12 is in contact with a source contact region 10, a depletion region 30 is extended simultaneously between the pillars. Alternatively, when the pillars 14 are in a floating state as discussed, a depletion region is extending differently from each of pillars 14 as shown with respect to depletion region 40. Thus, when a charge is balanced to maximize the breakdown voltage of a pillar 12 in contact with a source contact region 10, a charge compensation level becomes different. Hence, a breakdown voltage, generated vertically in the region 30, becomes lower than the breakdown voltage generated vertically in the region 40.
To address this issue, a pillar that is currently in a floating state is connected so as not to be in a floating state. However, in this situation, the horizontal length of the termination region is required to be longer. When the horizontal length of the termination region is not extended, a difference in charge compensation occurs as discussed further above or a problem of failing to provide a sufficient breakdown voltage occurs.